This invention relates to oscillating crystal transducer systems of the type described in my U.S. Pat. Nos. 4,703,216, 4,485,323, 4,439,705, 4,175,243, 4,126,801, 4,067,241, 4,020,488, and 3,891,870.
According to these patents a force or fluid pressure transducer contains one or more plate-like oscillating crystals which sit up-right on seatings disposed on a base member which forms part of the transducer housing. Means are provided for transmitting a force to the crystal along the direction of its surface in order to produce, in response to said force a change of the resonant frequencies of the crystal.
The force may originate from a fluid pressure where it is required to measure this pressure being applied to a diaphragm which forms part of the transducer enclosure. The center-point of this diaphragm is arranged to apply the force to the crystal.
In the later patents the crystal has on it two oscillating portions, one of which is substantially un-responsive to the force. This arrangement is advantageous because the change in difference frequency between the two portions is a very accurate measure of the force.
Although in principle, the existing patents disclosed transducers which performed with increasing accuracy over a progressively wider range of conditions as development proceeded, difficulty in manufacturing the units in a satisfactory manner and thereafter providing adequate hermetic sealing has continued to exists. The present invention provides means to overcome these problems.
The earlier problems were such as to make the transducers unduly bulky and as a result the masses of the components could result in excessive sensitivity to shock and vibration.
Further, although the required position of the crystal between its seatings was known, it was difficult to adjust the crystal into this position by this means to reduce inaccuracies resulting from ambient temperature changes.